Equipment for measuring gas flow rate

ABSTRACT

In a flow sensor, detecting elements are provided at a sub-passage. A sub-passage wall contains a hole to drain accumulated liquid. A protrusion arranged close to the hole on an external surface generates dynamic pressure on the opening in response to external flow. Alternatively, a protrusion upstream from the hole on the inner wall surface produces a separation flow area for separating the flow from the internal surface near the hole, whereby pressure in the separation area is reduced and almost the same pressure differences on the internal and external surfaces openings result. This reduces leakage from the hole and changes in the distribution flow in the sub-passage between cases where the hole is blocked and not blocked, thus minimizing flow measurement errors. Structure may be provided close to the external surface hole opening to prevent a liquid film or drop from being formed on the opening by surface tension.

FIELD OF THE INVENTION

The present invention relates to a gas flow measurement apparatus formeasuring a gas flow rate.

It particularly relates to a gas flow measurement apparatus having flowdetecting elements in a sub-passage through which part of the gas to bemeasured passes.

For example, it relates to a thermal resistor type air flow measurementapparatus for measuring the intake air flow rate in an automobileengine.

BACKGROUND OF THE INVENTION

As a thermal resistor type air flow measurement apparatus (gas flowmeasurement apparatus) for measuring the intake air flow rate taken intothe automobile engine, it is well-known that the apparatus is equippedwith a main passage in which the fluid to be measured flows and asub-passage in which part of the fluid flows. The flow detectingelements such as a heating resistor and a thermal sensitive resistor areset in the sub-passage.

Such a sub-passage type flow rate measurement apparatus can stabilizethe flow of the gas by utilizing the sub-passage structure. The flowdetecting elements can reduce that the flow detecting elements areaffected by the changes of the flow velocity distribution, by thepulsation flow and the back flow. Further, it can reduce thecontamination of the flow detecting elements, and thereby can reduce thedeterioration of quality of the elements. Further, in this apparatus,the flow detecting elements can be mounted easily on the main passageand protected effectively.

When, however, the internal configuration of the sub-passage changed dueto adherence of foreign substances, the measuring values of theapparatus will be increased over those of the gas flow measuringapparatus without sub-passage. To improve the function of thesub-passage, various modifications and improvements are incorporated inthe shape of the passage, and this tends to complicate the shape of thesub-passage. Especially in order to reduce the pulsating flow and tomaintain the measuring accuracy, the sub-passage is designed to have abent form, with the result that foreign substances tend to deposit inthe bent portion. The most probable trouble is that, depending on themounting angle of the flow measuring apparatus, such a liquid as waterwill accumulate in the sub-passage, or water remains in the bent portionof the curved sub-passage, thereby causing a flow measurement error.

To solve such problems, technical means are proposed to provide a drainhole for preventing water from remaining in the sub-passage, asdisclosed in the Japanese Application Patent Laid-Open Publication No.Hei 07-139414 and Japanese Application Patent Laid-Open Publication No.Hei 09-273950.

The flow measuring apparatus provided with such a drain hole is intendedto prevent from troubles caused by remaining of water in the sub-passageor submersion of the flow detecting elements in water.

The so-called leak hole (leak path) including the above-mentioned drainhole is a small hole that does not sacrifice the function of thesub-passage, and prevents from making water remain in the sub-passage.However, the last remaining liquid drop may remain inside the leak holedue to the surface tension.

Such a residual liquid drop such as waterdrop blocks the leak hole, andthis causes greater changes in air flow velocity distribution than thosewhen the leak hole is not blocked.

Such a phenomenon causes deterioration of accuracy and performancesincluding changes in the measurement value and increase of output noise.

The present invention has been made to solve these problems. It preventswater and other liquids from adhering and remaining in the sub-passage,and provides a sub-passage that minimizes the flow measuring errorcaused by liquid drops blocking the leak hole.

DISCLOSURE OF INVENTION

When water and other liquids have remained in the sub-passage, a flowmeasurement error will be smaller if such liquids are of smaller size.However, if liquid drops have collected to form big particles or theyhave accumulated in a particular portion, changes in the flow divisionratio will be caused by the changes in flow velocity distribution of thegas flowing in the sub-passage and changes in the resistance of thesub-passage to the flowing gas. This will result in a flow measurementerror.

Such remaining of liquid in the sub-passage can be avoided by providinga leak hole for leading the liquid out of the sub-passage so that theliquid can be drained out of the sub-passage, as described above.However, this leak hole must be designed to drain easily the liquid; forexample, it must have a specified sectional area.

On the other hand, to make full use of its functions, the sub-passagemust be designed so that gas flows inside as intended by the passage.The leak hole is the passage that does not meet the object of thesub-passage. It must have a structure that makes it hard for liquid toflow. This can be achieved, for example, by reducing the sectional areaof the leak hole.

To solve these problems, the present invention proposes the followingsolutions:

(1) The first of the present inventions provides a structural means,wherein a leak hole is provided to drain the liquid remained in thesub-passage, and the gas to be measured flowing in the sub-passagehardly flows through the leak hole.

In the first invention, a leak hole (through hole) between the internalsurface and the external surface of said sub-passage is provided enroute from the inlet of the said sub-passage to the outlet thereof; theopenings of said through hole is located on the internal surface and theexternal surface of said sub-passage, and a structural means forreducing the amount of the leak gas passing through said through hole isprovided close to at least one of said openings.

This configuration prevents water or other liquids from remaining in thesub-passage due to the leak hole. Further, even if the last liquid dropremaining subsequent to almost complete removing of liquid remains inthe leak hole due to surface tension, and thereby the leak hole isblocked, the measurement errors are prevented as follows. Thedistribution of air velocity in the sub-passage maintains anapproximately the same pattern in any case, since the status prior toblocking of the leak hole is so designed as to reduce the amount of flowthrough the leak hole. This configuration minimizes the difference offlow measurement errors between the cases where the leak hole is blockedand where not blocked.

(2) The above-mentioned leak hole is formed in such a size and shapethat the liquid does not remain in excess of the level where the affecton the flow measurement accuracy cannot be ignored.

As an embodiment for reducing the amount of gas passing through theabove-mentioned leak hole in the sub-passage, the present inventionproposes a structural means that generates the dynamic pressure close tothe opening of the leak hole on the external surface of the sub-passage.The dynamic pressure generates according to the velocity of the gas tobe measured, thereby increasing the pressure of that portion.Alternatively, it is also possible to assume that the portion close tothe opening of the leak hole on the internal surface of the sub-passageis formed as a separation flow area for separating the gas flow from theinternal surface of the sub-passage. Thereby, the pressure of that areais reduced, and the difference of the pressures inside and outside theleak hole is also reduced, the amount of the gas flowing through theleak hole is much reduced.

(3) To put it more specifically, the size of the leak hole is less thanone fifth of the sub-passage outlet area, such that the liquid is keptto remain there by the surface tension when there is a small amount ofthe remained liquid. For example, when the liquid consists of water, thediameter of the leak hole or the width of the shorter side of thereof is1 through 5 mm.

Further, a protrusion for generating the dynamic pressure is providedclose to the opening of the leak hole on the external surface of thesub-passage. This protrusion is intended to generate a dynamic pressureclose to the opening of the leak hole on the external surface of thesub-passage, according to the velocity of the gas flow through the mainpassage. When the shape and size of the protrusion is properly set, thedynamic pressure is adjusted so that the pressure differences generatedat the openings of the leak hole between the internal surface and theexternal surface of the sub-passage will be almost the same.

(4) To reduce the amount of the gas passing through the leak hole, aprotrusion is arranged upstream from the leak hole, on the internalsurface of the sub-passage. This protrusion is used in such a way thatthe portion close to the opening of the leak hole on the internalsurface of the sub-passage is formed as a separation flow area forseparating the gas flow from the internal surface of the sub-passage.Thereby, the pressure of that area is reduced to the level almost equalto the pressure close to the leak hole on the external surface of thesub-passage.

The liquid causing measurement errors is drained out of the sub-passageby the leak hole, on the one hand. For the gas, on the other hand, thepressures on both sides of the leak hole are almost the same, so thatthere is almost no flow of gas through the leak hole. That is, there ispractically no leak hole for gaseous fluids. This prevents the functionof the sub-passage from being deteriorated. Further, when the leak holeis blocked by water remaining there due to surface tension or the like,the gas flow is almost the same as that when the hole is not blocked.This configuration maintains required flow measurement accuracy.

(5) According to the second invention, a liquid film removing structureis provided to ensure that water and other liquids do not remain in theform of a liquid drop or liquid film due to surface tension or the likein the leak hole. This arrangement avoids a flow measurement error thatmay be occurred when the leak hole is blocked.

For example, the leak hole is designed to have such a size and shapethat do not affect the function of the sub-passage.

Further, the portion close to the opening of the leak hole on theexternal surface of the sub-passage is provided with the structuralmeans (e.g., a protrusion, plate-formed member and rod-formed member).When this arrangement has been made, the surface of the liquid drop orfilm formed in the leak hole hangs down, and when it comes in contactwith a plate- or rod-formed object, the liquid drop is pulled out by theobject, with the contact angle of the liquid drop on the surface of theobject. Thereby the liquid the liquid drop is prevented from remainingin the leak hole.

Another embodiment proposes an arrangement wherein the dynamic pressureof gas flowing through the sub-passage is applied to the opening of theleak hole on the internal surface of the sub-passage. Thus, the liquiddrop or the liquid film tending to remain in the leak hole is broken bythe dynamic pressure of gas.

For example, a partition wall is formed upstream from the leak hole inthe sub-passage to create a flow of gas moving toward the openingsurface of the leak hole on the internal surface of the sub-passage. Thedynamic pressure caused by flow of gas is formed on the opening surfaceof the leak hole on the internal surface of the sub-passage. Further,the end upstream from the partition wall is arranged to be the portionwhere higher pressure in the sub-passage is applied, thereby increasingthe pressure on the opening surface of the leak hole on the internalsurface wall surface of the sub-passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view and its partially enlarged viewrepresenting a gas flow measuring apparatus as a first embodiment of thepresent invention where the gas flow measuring apparatus is shown withthe cover removed;

FIG. 2 is an external view of this embodiment in FIG. 1 as viewed fromthe top (from the upstream side);

FIG. 3 is an external view of this embodiment in FIG. 1 as viewed fromthe left (bottom view);

FIG. 4 is an explanatory diagram of a gas flow measuring apparatus as acomparative example, showing how water remains in the sub-passagewithout a leak hole;

FIG. 5 is an explanatory diagram representing how water remains in thesub-passage with a leak hole;

FIG. 6 is a transverse cross sectional view and its partially enlargedview representing another form of the first embodiment;

FIG. 7 is a diagram representing the flow velocity vector of thesub-passage without dynamic plate;

FIG. 8 is a diagram representing the flow velocity vector of thesub-passage provided with dynamic plate;

FIG. 9 is a diagram representing the pressure distribution of thesub-passage without dynamic plate;

FIG. 10 is a diagram representing the pressure distribution of thesub-passage provided with dynamic plate;

FIG. 11 is a vertical sectional view representing the second embodimentof the present invention;

FIG. 12 is a partial side view representing the internal structure ofthe sub-passage of a gas flow measuring apparatus as a third embodimentof the present invention;

FIGS. 13 and 14 are partial side views representing the internalstructure of the sub-passage as another form of the third embodiment;

FIG. 15 is a diagram representing the flow velocity vector of thesub-passage without deflecting protrusion as a comparative example ofthe third embodiment;

FIG. 16 is a diagram representing the flow velocity vector of thesub-passage with deflecting protrusion in the third embodiment;

FIG. 17 is a diagram representing the pressure distribution of thesub-passage without deflecting protrusion;

FIG. 18 is a diagram representing the pressure distribution of thesub-passage with deflecting protrusion;

FIG. 19 is a partial side view of a gas flow measuring apparatus as afourth embodiment of the present invention;

FIG. 20 is a bottom view of the same;

FIG. 21 is a partial side view of a fifth embodiment of the presentinvention; and

FIG. 22 is a vertical sectional view representing a sixth embodiment ofthe present invention.

BEST FORM OF EMBODIMENT OF THE PRESENT INVENTION

The first embodiment of the present invention will be describedhereinafter with reference to FIGS. 1 through 3 and 6. Further, FIGS. 4and 5 will be used to describe the state of water remaining in thesub-passage in the prior art example and the present embodiment.Further, the function of this embodiment will be described based on theresult of flow analysis according to FIGS. 7 through 10.

FIG. 1 is a cross sectional side view and its partially enlarged viewrepresenting a thermal resistor type air flow measurement apparatus formeasuring the air flow rate taken into an automobile engine, wherein thegas flow measurement apparatus is shown with the cover removed.

The air flow measurement apparatus (gas flow measurement apparatus)comprises of a main passage 8 through which an intake air as a gas to bemeasured flows, and a sub-passage 4 through which part of the intake airflows. The sub-passage 4 is provided in the main passage 8.

In this embodiment, a heating resistor 1, a thermo-sensitive resistor 2and an intake air temperature measuring element 3 are fixed to eachterminal 11 so that they are located inside the sub-passage 4, and areelectrically connected with an electronic circuit 5.

The electronic circuit 5 controls the heating temperature of the heatingresistor 1, based on the intake air temperature detected by thethermo-sensitive resistor 2. For example, the current (heating current)flowing to the heating resistor 1 is controlled so that the temperaturedifference between the heating resistor 1 and thermo-sensitive resistor2 will reach a predetermined temperature difference level. The amount ofheat radiated from the heating resistor 1 is approximately proportionateto the air flow rate, so the electric signal corresponding to the airflow rate can be sent via a connector 9 to the external equipment bydetecting the heating current. In the present embodiment, this method isused to measure the air flow rate. It is also possible to locatethermo-sensitive resistors on upstream and downstream from the heatingresistor, and to measure the air flow rate based on the temperaturedifference between the two resistors. There is no restriction on themethod of measurement.

The signal of intake temperature measuring element 3 can be used fortemperature correction of the thermo-sensitive resistor 2 or for otherpurposes.

A housing 6 is a plastic component molded with inserting such metalliccomponents as the terminal 11. It is an united formation of a casemember 6 a forming a frame for incorporation and protection of theelectronic circuit 5, a connector 9 for electric connection with anexternal device, and a flange member 10 for fixing onto a member 7constituting the main passage 8.

The sub-passage 4 is a plastic molded product, and is connected to thehousing 6 or is formed integrally with the housing 6. Thus, the housing6 and sub-passage 4 are integrally structured in parallel arrangement.

The electronic circuit 5 is installed inside the case member 6 a of thehousing 6 and is protected by attaching a cover 12 to the housing 6 soas to cover the case member 6 a, as shown in FIG. 2.

Accordingly, the electric circuit, the detecting elements, thesub-passage and the connector are formed in an integral module.

The sub-passage 4 is serially formed by;

an air flow inlet 401 opening on the plane approximately perpendicularto the main flow direction 13 of air passing through the main passage;

a first flow path 402 parallel to the main flow direction 13;

a first bent portion 403 bending approximately perpendicular to the mainflow direction 13;

a second bent portion 404 further bending approximately perpendicularly;

a second flow path 405 which is arranged in parallel with the first flowpath 402, and lets the air flow turned over through these bent portionspass;

an air flow outlet 406 opening on the plane approximately parallel tothe main flow direction 13 at the downstream of the path 405 (it'slocated in an upper side in the main flow direction 13). Thus thesub-passage 4 forms a U-shaped circuitous passage.

The heating resistor 1, the thermo-sensitive resistor 2 and the intaketemperature measuring element 3 are provided in the first flow path 402.

Further, in the sub-passage 4, a leak hole (through hole) 407 and aplate-formed projection (hereinafter referred to as “dynamic pressureplate”) 408, which are major points of the present invention, areprovided at the bent portion 404. They are formed integrally with thewall of the sub-passage 4.

The leak hole 407 opens on the internal surface and the external surfaceof the sub-passage 4, thereby the sub-passage 4 communicates with themain passage. The cross section of the leak hole 407 can be designed incircular, rectangular and many other forms. In the present embodiment,an oblong slit is used as a leak hole, and its size is determined on theorder of millimeters. For example, the shorter side is about 2 mm long.The longer side is set to the width of the sub-passage (See FIG. 3). Thesize of this leak hole is determined as desired, with reference to sizesof the sub-passage, the main passage and the dynamic pressure plate 408.

The dynamic pressure plate 408 is located on the plane (base of theexternal surface of the sub-passage) 409 parallel to the main flowdirection on the external surface of the sub-passage 4. It is arrangedclose to the opening of the leak hole 407 on the external surface of thesub-passage. When the upstream and downstream sides in the direction ofthe main flow 13 is defined, with reference to the position of theopening of the leak hole 407 on the external surface of the sub-passage,the dynamic pressure plate 408 is formed so as to protrude from the base409 of the external surface of the sub-passage at the position of thedownstream side.

This dynamic pressure plate 408 serves as an obstacle to the main flow13. When the main flow 13 is received by this obstacle, the dynamicpressure occurs at the opening of the leak hole 407 on the externalsurface of the sub-passage (leak hole outlet).

In the present embodiment, the dynamic pressure plate 408 is formed sothat the surface 408 a facing to the upstream side of the main passageis perpendicular to the main flow. The height “h” of the dynamicpressure plate 408 (distance from the opening of the leak hole 407 onthe external surface of the sub-passage to the protruded end of thedynamic pressure plate 408) is set, for example, to about 0.5 through 2times the length W of the short side of the leak hole 407 (diameter ifthe leak hole is circular). Here the optimum value is 2.5 through 3.0mm.

The dynamic pressure plate 408 is used as a structural means to ensurethat the leakage of air passing through the leak hole 407 is decreasedby minimizing the difference between the pressure close to the secondbent portion 404 in the sub-passage 4 (on the opening of the leak hole407 on the internal surface of the sub-passage) and the pressure on theopening of the leak hole 407 on the external surface of the sub-passage.

The main passage 8 is used as the flow path through which the air to bemeasured passes. In the case of a car engine, for example, itcorresponds to the intake pipe located from an air cleaner to theupstream of the engine cylinder. In the thermal resistor type air flowmeasurement apparatus for automobile, the member 7 constituting thismain passage 8 is located on the midpoint of the intake pipe for thebody of the measurement apparatus use only in some cases. The member 7may be used both as the main passage 8 and an air cleaner or duct orthrottle body etc. in other cases.

An insertion hole 15 for positioning a measuring module (the modulecomprising of the detecting elements such as the heating resistor 1 andthe thermo-sensitive resistor 2, the sub-passage 4, housing 6 andothers) to inside of the main passage 8 is provided at the wall of themain passage member 7. The measuring module is provided by fixing thehousing 6 at the main passage member 7 with a screw or the like. Thus,the amount of the intake air passing through the main passage can bemeasured.

In the case of an air flow measurement apparatus without theabove-mentioned leak hole 407, if water from the outside enters tosub-passage 4, water may remains in the sub-passage 4, depending on theinstallation angle.

FIG. 4 shows how water remains.

FIG. 4 shows a circuitous sub-passage 4 without a leak hole. Itrepresents the case where the air flow measurement apparatus isinstalled when water is likely to remain in the second bent portion 404(passage bend angle).

In this case, water entering the sub-passage 4 remains close to thesecond bent portion 404. Since the sectional area of the sub-passage 4is reduced close to water area 16, there is an increase in theresistance to air flow in the sub-passage 4, and there is a decrease inthe amount of air flowing through the sub-passage 4 (the air flow rateof the main passage is increased and the air flow rate of thesub-passage is decreased, even if the flow of air to be measured is thesame). Thus, a large negative error occurs in the air flow rate measuredby the air flow measurement apparatus.

If the amount of the remained water increases by accumulating accordingto the shape or the installation angle of the sub-passage, thesub-passage 4 will be partially blocked with water. Thereby the air cannot flow into the sub-passage 4, and the air flow cannot be measured.That is, it is also possible that the air does not pass through thesub-passage 4, and the output to indicate the air flow rate becomes zerodue to error.

Further it is also possible that, if detecting elements 1, 2 and 3 aresoaked in water, a serious measurement error occurs and the detectingelements 1, 2 and 3 are damaged by corrosion and electrolytic corrosion,thereby the measurement is disabled.

By contrast, in the case of a sub-passage 4 with leak hole 407, waterentering the sub-passage 4 flows out through the leak hole 407 as shownin FIG. 5. Thus, the situation where the flow of air in the sub-passage4 is shut off can be prevented. According to the installation angle andshape of the sub-passage 4A, plural leak holes 407 may be provided atthe position where water may remain.

When the amount of water entering the sub-passage 4 is much reduced asshown in FIG. 5, the surface tension in the leak hole allows water toremain in the state of waterdrop 16 or water film. When the amount ofwater 16 is increased, it gets stronger than the surface tension, andwater flows out through the leak hole 407. In this case, water alsoremains in the state of waterdrop or water film when the amount of waterbecomes very little.

As described above, in the sub-passage 4 provided with a leak hole 407,water does not remain so much that it hinders the flow of air in thesub-passage 4 even if water enters to the sub-passage 4. However, theleak hole 407 is blocked by water 16. In this case, there is no leakageof air flowing out of the sub-passage (main passage) through the leakhole 407. Accordingly, there is a change in the flow of air in thesub-passage 4 as compared to the case where the leak hole 407 is notblocked by water. Such a situation causes an error in air flowmeasurement.

In this embodiment, such an air flow measurement error can be reduced asfollows.

The position close to the second bent portion 404 in the sub-passage 4(close to the opening of the leak hole 407 on the internal surface ofthe sub-passage) is an area where dynamic pressure is generated. Thepressure in the area is comparatively high in the sub-passage 4. On theother hand, the position close to the opening of the leak hole 407 onthe external surface of the sub-passage belongs to the low pressure areadue to the velocity of the main flow 13 along the external wall of thesub-passage if there is no dynamic pressure plate 408. However, in caseof providing a dynamic pressure plate 408, dynamic pressure isgenerated. Thereby, since the pressure difference between the opening ofthe leak hole 407 on the external surface of the sub-passage and thearea close to the second bent portion 404 is almost equivalent, the airleakage in the sub-passage 4 is decreased effectively even if the leakhole 407 is not blocked by water.

Accordingly, since there is not much change in the distribution of theair flow between the case where the leak hole 407 is blocked with waterand the case where it is not blocked, air flow measurement errors areminimized.

In FIG. 1, the dynamic pressure plate 408 is formed so that the surface408 a facing toward the upstream (air inlet side) of the main passage 8is perpendicular to the main flow 13. However, instead of it, as shownin FIG. 6, the surface 408 a facing toward the upstream of the mainpassage 8 may incline toward the direction of forming an acute angle tothe external surface of the sub-passage (direction of facing slightlytoward the side of the leak hole 407). Thus, dynamic pressure can begenerated effectively to the opening of the leak hole 407 on theexternal surface of the sub-passage by forming an inclined surface onthe dynamic pressure plate 408.

In case of the dynamic pressure plate 408 in FIG. 6, even if the height“h” of the plate 408 is shorter than that of the dynamic pressure plate408 in FIG. 1, it can generate the dynamic pressure equivalent to theplate of FIG. 1. In case of the embodiment in FIG. 6, the optimum valueof the height “h” of the dynamic plate can be set to 0.5 through 2.0 mmwhen the short side of the leak hole 407 is 2 mm.

The advantage of the dynamic pressure plate 408 of the presentembodiment will be described with reference to the flow analysis resultgiven in FIGS. 7 through 10.

FIG. 7 is a diagram representing the flow velocity vector in thecomparative example of the sub-passage 4 (although it has the leak hole407 but it does not have the dynamic pressure plate 408). It shows theresult of the flow analysis when the average flow velocity of the mainpassage (main flow) is 2 m/s. In this case, the flow of velocity of 1m/s or more occurs in the area ranging from the leak hole 407 to themain passage.

FIG. 8 is a diagram representing the flow velocity vector in thesub-passage 4 provided with the dynamic plate 408 of the presentinvention (the plate 408 whose surface facing the upstream side of themain flow forms an inclined surface), FIG. 8 is drawn by the graphcorresponding to FIG. 6.

In this case, the pressure difference on the openings of the leak hole407 on the internal surface and the external surface of the sub-passage,namely both ends of the leak hole 407, can be reduced by the function ofthe dynamic pressure plate 408. Thereby, the flow velocity of airflowing out from the leak hole 407 is reduced below 0.5 m/s.

FIG. 9 is a diagram representing the pressure distribution inside andoutside the sub-passage surrounding the leak hole 407 in the comparativeexample given in FIG. 7. FIG. 10 is a diagram representing the pressuredistribution inside and outside the sub-passage surrounding the leakhole 407 in the embodiment given in FIG. 8. FIGS. 9 and 10 show theresult of the flow analysis when the average flow velocity in the mainpassage is 2 m/s.

As shown in FIG. 9, when the leak hole 407 is not provided with thedynamic plate, the pressure on the opening 4 of the leak hole 407 on theinternal surface of the sub-passage is negative. The pressure differenceon the openings of the leak hole 407 on the internal surface and theexternal surface of the sub-passage 4 is 0.5 Pa or more.

On the other hand, in FIG. 10, the dynamic pressure is generated on theopening of the leak hole 407 on the external surface of the sub-passage,by the dynamic pressure plate 408. Thereby, the pressure on the openingis increased. That is, the dynamic pressure is generated in response tothe air flow close to the side wall 409 of the sub-passage by the plate408, around the opening of the leak hole 407 on the external surface ofthe sub-passage. The dynamic pressure increases the pressure close tothe opening of the leak hole 407 on the external surface of thesub-passage. Accordingly, the pressure difference on the openings of theleak hole 407 on the internal surface and the external surface of thesub-passage 4 is reduced below 0.2 Pa.

In such a configuration, the difference between the maximum pressureclose to the opening of the leak hole 407 on the internal surface of thesub-passage and the minimum pressure close to the opening on theexternal surface of the sub-passage is kept at a level not exceeding theone fifth of the u²/2 g. The u²/2 g is a value of the dynamic pressuregenerated by the average flow velocity “u” of the gas to be measured.

Further, the difference between the detected flow rates where the leakhole is blocked and where not blocked can be made 2% or less.

The second embodiment will be described with reference to FIG. 11:

FIG. 11 is a sectional view representing a thermal resistor type airflow measurement apparatus having the sub-passage 4 which is not bent.The sub-passage 4 has a flow contraction section 4′ formed between theinlet opening 401 and the outlet opening 406. The flow detectingelements 1 and 2 are set downstream from the flow contraction section4′.

In such a sub-passage, water may remain in the flow contraction section4′, so the leak hole 407 is provided on the bottom of the section 4′,and the dynamic pressure plate 408 is formed downstream from the leakhole 407.

In the air flow measurement apparatus of the present embodiment, whenwater has entered the sub-passage 4, the remained water area 16 islikely to be formed close to the bottom of the flow contraction section4′ in some cases, if there is no leak hole 407. The remained water area16 may hinder air flow. It may change the flow distribution of the flowvelocity at the location of the flow detecting elements 1 and 2, or mayaffect the flow division ratio of the sub-passage 4.

In the present embodiment, accumulating of water in the sub-passage 4can be avoided by the leak hole 407. When the leak hole 407 is blockedby the waterdrop or the water film, the flow measurement error mayoccur. However, according to the same dynamic pressure generationprinciple as that of the aforementioned embodiment, there is not muchchange in the distribution of air flow velocity between the cases wherethe leak hole is blocked and where not blocked. This arrangement canreduce air flow measurement errors.

FIG. 12 is a partial cross section representing a third embodiment ofthe present invention. The basic configuration of the air flowmeasurement apparatus is the same as that given in FIG. 1. Namely, inthe present embodiment, similarly to the embodiment given in FIG. 1, theheating resistor 1, the thermo-sensitive resistor 2 and the intaketemperature measuring element 3 are fixed to the terminal 11 so thatthey are located inside the sub-passage 4, and are electricallyconnected with the electronic circuit 5. The sub-passage 4, theelectronic circuit 5, the connector 9, the housing 6, the cover 12 andthe main passage 8 are omitted in FIG. 11.

The major shape of the sub-passage 4 is the same as that of FIG. 1. Theleak hole 407 and the dynamic pressure plate 408 are provided.

In the present embodiment, in addition to the above, a protrusion 411having a triangular cross section (angular form) is provided close tothe position upstream from the leak hole 407 in the sub-passage 4. Theprotrusion 411 has inclinations that faces upstream and downstream ofthe sub-passage 4. The protrusion 411 may have one inclination. Theprotrusion 411 deflects the flow of air passing through the sub-passage4. This is called the deflecting protrusion 411.

The deflecting protrusion 411 is formed on the internal surface close tothe second bent portion 404 in the sub-passage 4. In other words, here,when the upstream and the downstream in the sub-passage are defined onthe basis of the opening of the leak hole 407 on the internal surface ofthe sub-passage, the deflecting protrusion 411 is formed upstream fromthe opening. The protrusion 411 is close to the opening of the leak hole407 on the internal surface of the sub-passage.

Accordingly, the direction of the air flowing in the sub-passage 4 closeto the wall surface of the deflecting protrusion 411 is further changedtoward the outlet opening 406 of the sub-passage. Thus, the area closeto the opening of the leak hole 407 on the internal surface of thesub-passage becomes an area for separating the air flow from theinternal surface. Thereby, the pressure of that area is reduced.

As a result, in addition to the aforementioned function of the dynamicpressure plate 408, the pressure close to the opening of the leak hole407 on the internal surface of the sub-passage becomes almost equal tothe pressure close to the opening on the external surface of thesub-passage. Thereby, the air flow which flows through the sub-passage,when the leak hole 407 is blocked and when not blocked, is maintained atthe almost same state. Accordingly, the measurement errors, that may becaused by water 16 in the form of the waterdrop and the water filmremaining in the leak hole 407, can be reduced.

FIG. 13 shows another form of the embodiment given in FIG. 12. Thedifference from FIG. 12 is that the dynamic pressure plate 408 isprovided with an inclined surface similar to the one given in FIG. 6.

FIG. 14 also shows another form of the embodiment given in FIG. 12. Thedifference from FIG. 12 is that the dynamic pressure plate 408 is notprovided, and only the deflecting protrusion 411 is used to reduce thepressure close to the opening of the leak hole 407 on the internalsurface of the sub-passage. Thereby this pressure approaches the levelof the pressure close to the opening of the leak hole 407 on theexternal surface of the sub-passage.

The effect of the deflecting protrusion 411 in the present embodimentwill be described with reference to the flow analysis result given inFIGS. 15 through 18.

FIG. 15 is a diagram representing the flow velocity vector in thesub-passage, wherein the sub-passage 4 is used for the air flowmeasurement apparatus of the embodiment of FIG. 6 (the sub-passage isprovided with the leak hole 407 and the dynamic pressure plate 408, butnot with a deflecting protrusion 411). It is represented in the form ofa cross section parallel to the main flow, and shows the result of theflow analysis when the average flow velocity of the main passage is 25m/s.

FIG. 16 is a diagram representing the flow velocity vector in thesub-passage, wherein the sub-passage 4 is used for the air flowmeasurement apparatus of the embodiment given in FIG. 13 (provided withthe leak hole 407, the dynamic pressure plate 408 and the deflectingprotrusion 411). It is represented in the form of a cross sectionparallel to the main flow, and shows the result of flow analysis whenthe average flow velocity of the main passage is 25 m/s.

As shown in FIG. 15, when there is no deflecting protrusion 411, thevelocity of the fluid flowing out from leak hole 407 is on the order of15 m/s even when the advantage of the dynamic pressure plate 408 isutilized. By contrast, when the deflecting protrusion 411 is provided,the velocity of the fluid flowing out from the leak hole 407 is reducedto about 7 m/s. This ensures a further reduction of the flow measurementerrors even when a leak hole is provided.

FIG. 17 is a diagram representing the pressure distribution around theleak hole 407 of the sub-passage 4 in the air flow measurement apparatusgiven in FIG. 15. FIG. 18 is a diagram representing the pressuredistribution around the leak hole 407 of the sub-passage 4 in the airflow measurement apparatus given in FIG. 16. They show the result of theflow analysis when the average flow velocity of the main passage is 25m/s.

As shown in FIG. 17, when the deflecting protrusion 411 is not provided,the pressure difference between the openings of the leak hole 407 on theinternal surface and external surface of the sub-passage 4 is 40 Pa ormore. As shown in FIG. 18, when a deflecting protrusion 411 is providedupstream from the leak hole 407 in the sub-passage 4, the pressure closeto the opening of the leak hole 407 on the internal surface of thesub-passage is reduced. The pressure difference between the openings ofthe leak hole 407 on the internal surface and the external surface ofthe sub-passage is on the order of 25 Pa.

The aforementioned embodiments intend to minimize the flow measurementerror even when water remains in the leak hole 407 due to the surfacetension and others, and even when the leak hole is blocked.

In the embodiments of FIG. 19 and thereafter, they describe a structurefor eliminating liquid films from the leak hole. These embodimentsactively prevent water from remaining in the leak hole 407 due tosurface tension and others, so the flow measurement errors will notoccur due to the leak hole being blocked.

FIG. 19 is a cross section showing the major portion of an air flowmeasurement apparatus as a fourth embodiment of the present invention.The electronic circuit 5, the connector 9, the housing 6, cover 12 andmain passage 8 as shown in FIG. 1 are omitted. They have the sameconfiguration as those of the aforementioned embodiments. FIG. 20 showsthe bottom view thereof.

The arrangements of the flow detecting elements such as heating resistor1 etc. and overall profile of the sub-passage 4 in the presentembodiment are the same as those of the embodiments described withreference to FIGS. 1 through 18, so they will be omitted in thefollowing description to avoid duplication.

In the present embodiment, a means for preventing the liquid film beingformed on the opening by surface tension is provided close to theopening of the leak hole 407 on the external surface of the sub-passage.

A plate-formed member 412 (or a rod-formed member) facing this opening,for example, is used as the liquid film preventing means. It is locatedat a position just coming out of the opening of the leak hole 407 on theexternal surface of the sub-passage.

The plate-formed member 412 is integrally formed with a protrusion piece420 additionally provided on the bottom 409 of the sub-passage 4. Theprotrusion piece 420 is formed integrally with the sub-passage 4 so thatit extends at a long side of the body of the sub-passage 4. Theplate-formed member 412 is also intersects at right angles with theprotrusion piece 420.

The plate-formed member 412 (or the rod-formed member) is located on theextension approximately of the center line of the opening of the leakhole 407 on the external wall surface of the sub-passage.

Further, a gap G is provided between the end plane of the plate-formedmember 412 and the opening of the leak hole 407 on the external surfaceof the sub-passage. This is because the liquid film cannot be removedfrom the leak hole 407, if the end of the plate-formed member 412 hasreached the opening of the leak hole 407 on the external surface of thesub-passage or it is inserted into the leak hole beyond the opening.Since a certain gap G is kept between the opening of the leak hole 407on the wall surface of the sub-passage and the end of the plate-formedmember 412, it is easy to break the liquid film as follows. That is,since the waterdrop comes into contact with the protrusion 412 as ithangs down from the outlet side opening of the leak hole 407, thewaterdrop breaks easily.

When water has accumulated in the sub-passage 4, the leak hole 407drains water away to the outside. In the case of a leak hole having thehole size that does not deteriorate the function of the sub-passage 4,water in the form of waterdrop and water film remains in the leak hole407, as shown in FIG. 5. The flow of air through the sub-passage isaffected, as compared to the case where no water remains, andmeasurement errors will occur, as described earlier.

In the present embodiment, when the waterdrop have grown in the leakhole 407, its surface contacts the plate-formed member 412, and thewaterdrop is pulled out toward the plate-formed member by the contactangle of the waterdrop to the surface of the plate-formed member 412.Therefore, the waterdrop large enough to block the leak hole 407 comesin contact with the plate-formed member 412 and tends to come out alongthe plate-formed member 412. Accordingly, it is possible to preventwater from remaining in the leak hole 407.

FIG. 21 shows an embodiment that provides a structure for preventing thewater film and the water drop in the leak hole 407, similarly to FIG.19.

In the present embodiment, a partition wall 413 is formed integrallywith the sub-passage 4. The partition wall 413 separates the flow of gasaround the second bent portion 404 of the internal surface of thesub-passage 4, and leads part of the flow to the leak hole 407.

The separated passage 415 formed by the partition wall 413 and theinternal surface of the sub-passage 404 is located upstream from theleak hole 407. The partition wall 413 ends immediately before the leakhole 407, and the ended portion 414 communicates with the second bentportion 404. The ended portion 414 allows smooth feeding of waterthrough the separated passage 415 formed by the partition wall 413,thereby leading it to the leak hole 407.

According to the aforementioned configuration, the partition wall 413separates part of air flowing through the sub-passage 4, and leads theflow of air straight into the leak hole 407, whereby dynamic pressure isgenerated on the opening of the leak hole 407 on the internal surface ofthe sub-passage. In particular, the upstream end of the partition wall413 is located so as to face the bent portion having a higher pressurein the sub-passage 4. This configuration can further increase thepressure generated on the opening of the leak hole 407 on the internalsurface of the sub-passage.

As described above, the leak hole 407, having a small opening areawithout affecting the function of the sub-passage 4, allows thewaterdrop and the water film to drain to the outside by the pressuregenerated on the opening of the leak hole 407 on the internal surface.Since the leak hole is open at all times (without being blocked byliquid), it is possible to prevent the flow measurement errors that maybe caused by change of gas flow resulting from the leak hole beingblocked.

FIG. 22 shows an embodiment wherein a deflecting protrusion 411 and thedynamic pressure plate 408 are formed onto the flow measurementapparatus having the same configuration as that of FIG. 11. In such aconfiguration, the direction of air flowing through the sub-passage 4close to the leak hole 407 is changed toward the center of thesub-passage 4, similarly to the case of the embodiment described withreference to FIG. 11. Thus, the portion close to the opening of the leakhole 407 on the internal surface becomes an exfoliation flow area, wherethe pressure is reduced, accordingly the pressures inside and outsidethe leak hole 407 are almost the same with each other. Thisconfiguration allows almost the same flow to be kept between the caseswhere the leak hole 407 is blocked and where not blocked. Thereby themeasurement errors, that may be caused by the waterdrop and the waterfilm remaining in the leak hole 407, are reduced.

If the area around the leak hole of the aforementioned sub-passage, theprotrusion, the plate- or the rod-formed member or the partition wallfor generating the dynamic pressure or the exfoliation area has asurface coarser than other portions, the following effect can beexpected. According to the configuration, since the contact angle ofliquid on their surface is reduced, water can be easily drained from theleak hole.

In the aforementioned embodiments, we could get preferable results whenthe diameter of the leak hole 407 or the length of the short side was0.5 through 2 times the height of the liquid drop produced by thesurface tension of the liquid such as water entering the sub-passage.

INDUSTRIAL FIELD OF APPLICATION

The present invention can prevent water from remaining in thesub-passage by making water drain through the leak hole, even if watertends to accumulate due to entering into the sub-passage or due tocondensing inside the sub-passage. Further, the present inventionreduces a flow measurement error, independently of whether or not theleak hole is blocked by a liquid film or liquid drop (adhering to theleak hole without remaining in the sub-passage) formed therein. Or theinvention prevents the liquid film such as water film from accumulatingin the leak hole at all times, thereby reducing the flow measurementerror and improving the flow measurement accuracy. Moreover, the presentinvention provides such advantages without affecting the cost, size,weight and others.

1.-30. (canceled)
 31. A gas flow measurement apparatus, comprising: amain passage for making a gas flow, a sub-passage for making part of thegas flow; and gas flow detecting elements which are provided at saidsub-passage for detecting a gas flow rate, wherein a through holebetween the internal surface and the external surface of saidsub-passage is provided en route from the inlet of the said sub-passageto the outlet thereof, and a gas flow structure in said sub-passage ismade so that the opening of said through hole on the internal surface ofsaid sub-passage becomes a separation flow area for separating the gasflow from said internal surface.
 32. A gas flow measurement apparatus,comprising: a main passage for making a gas flow, a sub-passage formaking part of the gas flow; and gas flow detecting elements which areprovided at said sub-passage for detecting a gas flow rate; wherein athrough hole between the internal surface and the external surface ofsaid sub-passage is provided en route from the inlet of the saidsub-passage to the outlet thereof; a deflecting structure for changingthe direction of the gas flow in the sub-passage is provided upstream ofsaid through hole on the internal surface; and the opening of saidthrough hole on the internal surface of said sub-passage is formed as aseparation flow area for separating the gas flow from the said internalsurface by said deflecting structure.
 33. The gas flow measurementapparatus according to claim 32, wherein said deflecting structure is aprotrusion formed on the internal surface of said sub-passage upstreamfrom said through hole.
 34. The gas flow measurement apparatus accordingto claim 33, wherein said protrusion are inclined on the surface of theupstream side or both surfaces the upstream and downstream sides. 35.The gas flow measurement apparatus according to claim 33, wherein theheight of said protrusion is about 0.5 through 2 times the diameter ofsaid through hole or the length of the short side of said through hole.36. A gas flow measurement apparatus, comprising: a main passage formaking a gas flow, a sub-passage for making part of the gas flow; andgas flow detecting elements are provided at said sub-passage fordetecting a gas flow rate, wherein a through hole between the internalsurface and the external surface of said sub-passage is provided enroute from the inlet of the said sub-passage to the outlet thereof, apartition wall is formed inside said sub-passage, and said partitionwall separates the gas flow in said sub-passage and leading part of thegas flow to the through hole.
 37. The gas flow measurement apparatusaccording to claim 36, wherein said partition wall ends immediatelybefore said through hole, and the ended portion communicates with saidsub-passage.
 38. The gas flow measurement apparatus according to claim36, wherein said sub-passage contains a section for generating dynamicpressure through the gas flowing through said sub-passage, and saidpartition wall is formed from the dynamic pressure generating sectiontoward said through hole.